Annite is a dark, iron-rich member of the mica group commonly found in igneous rocks like granites and syenites. It is easily recognized by its dark, often black, micaceous sheets that show perfect cleavage, though it is often chemically indistinguishable from other biotite-series minerals without laboratory analysis.
Is this annite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch annite with a known reference. Annite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black, reddish brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, foliated masses, micaceous scales.
Often confused with
Annite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Annite leaves brownish white, Phlogopite leaves white; luster reads vitreous on Annite and pearly to submetallic on cleavage on Phlogopite.
How to tell apart: Streak differs, so Annite leaves brownish white, Siderophyllite leaves greenish gray.
How to tell apart: Streak differs, so Annite leaves brownish white, Muscovite leaves white.
Often found alongside annite
Minerals reported to co-occur with annite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KFe₃AlSi₃O₁₀(OH)₂
- Mohs hardness
- 2.5-3
- Density
- 3.3 g/cm³
- Colors
- Streak
- Brownish white
- Luster
- Vitreous
- Transparency
- Translucent to transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, foliated masses, micaceous scales
- Cleavage
- Perfect on {001}
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- In magnesium-poor igneous and metamorphic rocks
Where rockhounds find annite
Classic worldwide localities
- Cape Ann, east of Rockport, Essex Co., Massachusetts, and on Pikes Peak, El Paso Co., Colorado, USA
- Mont Saint-Hilaire, Quebec, Canada
- Moina tungsten skarn deposit, 40 km southwest of Devonport, Tasmania
- Kawai mine, Ena, Gifu Prefecture, Japan
- Katugin, Siberia, and Sludorudnik, Ural Mountains, Russia
- Flowerdale, near Gairloch, Scotland
Field-hunting tip
Where it forms: In magnesium-poor igneous and metamorphic rocks. If you start seeing zircon in float, you are in the right ground. Typical habit: tabular crystals, foliated masses, micaceous scales. Train your eye for that shape before scanning the outcrop.
Common questions
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Find annite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
